A. Field of Invention
The invention relates to a continuously operating press, preferably for the manufacture and/or printing, lamination or the like of a one or multiple layer board web of pre-manufactured material and/or raw material. Such presses are particularly used for the manufacture of particleboard, fiberboard, hardboard or the like, and indeed from a mat comprising particles containing lignocellulose and/or cellulose such as wood chips, wood fibers or the like and at least one dispersed binder. The mat runs in the transport direction between the upper run of a lower endless press band and the lower run of an upper endless press band which are preferably of steel and which circulate at a predetermined speed. A slide coating with grooves is provided on upper and lower abutments or supports and extends over the entire width of the press zone. The press zone comprises at least one main press zone and a calibration zone which follows the latter. In operation each press band slides over the slide coating by means of a lubricant which is supplied under pressure and is optionally heated or cooled. The lubricant is supplied via feed lines and supply openings in the slide coating, and is led away through discharge openings and also discharge lines which are connected thereto. The lubricant is supplied to the press anew in a circuit--optionally after being heated or cooled again. Each groove of the slide coating has only one opening, with one of the supply openings being provided in the one groove and one of the discharge openings being provided in the groove adjacent thereto, pressure control means for generating a counter-pressure are associated with each groove having a discharge opening or a supply opening.
B. Description of the Related Art
A press of the above described kind is known from U.S. Pat. No. 4,565,509. This latter U.S. Patent also refers to an earlier U.S. Pat. No. 4,420,299 which illustrates a typical continuously operating press with recirculating steel press bands. The contents of these two U.S. specifications are incorporated herein by reference.
In the press known from U.S. Pat. No. 4,565,509 the pressure control means for the lubricant for generating a counter-pressure in the working gap of the press (which pressure control means are associated with each groove of the slide coating having a discharge opening or a supply opening), ensure that the surface forces acting on the press band and on the slide coating are more uniformly carried by the lubricant. This results in an extremely low coefficient of friction and a correspondingly uniform heating or cooling distribution of the lubricant which is an important factor in determining the quality of the pressed material. A further determining factor for the quality is moreover the maintenance of a constant thickness and speed of the lubricant pressure film. This requirement cannot be straightforwardly and sufficiently satisfied in practice for the most stringent demands, even when the pressure control means for the lubricant are ideally adjusted for the generation of a counter-pressure in the working gap of the press.